TDataSet.FindField Method

Searches for a specified field in the dataset.

Pascal

function FindField(const FieldName: string): TField;

C++

__fastcall TField FindField(const AnsiString FieldName);

Description

Call FindField to determine if a specified field component exists in a dataset. FieldName is the name of the field for which to search. This name can be the the name of a simple field, the name of a subfield of an object field that has been qualified by the parent field's name, or the name of an aggregated field.

If FindField finds a field with a matching name, it returns the TField component for the specified field. Otherwise it returns nil (Delphi) or NULL (C++).

FindField is the same as the FieldByName method, except that it returns nil (Delphi) or NULL (C++) rather than raising an exception when the field is not found.

C++ Examples:

Copy Code

/*
This example uses a button to copy the value of a field in
the previous record into the corresponding field in the
current record.  The field to copy is specified by using
FindField and the name of the field.
*/
void __fastcall TForm1::Button2Click(TObject *Sender)
{
  TBookmark SavePlace;
  Variant PrevValue;
  // get a bookmark so that we can return to the same record
  SavePlace = Customers->GetBookmark();
  try
  {
    // move to prior record}
    Customers->FindPrior();
    // get the value
    // This is the safe way to get 'CustNo' field
    PrevValue = Customers->FindField("Field2")->Value;
    // This is *not* the safe way to change 'CustNo' field
    // PrevValue = Customers->Fields->Fields[1]->Value;
/*
    Move back to the bookmark
    this may not be the next record anymore
    if something else is changing the dataset asynchronously
*/
    Customers->GotoBookmark(SavePlace);
    // Set the value
    Customers->Edit();
    // This is the safe way to change 'CustNo' field
    Customers->FindField("Field2")->AsString = PrevValue;
    // This is *not* the safe way to change 'CustNo' field
    // Customers->Fields->Fields[1]->AsString = PrevValue;
    // Free the bookmark
  }
  __finally
  {
    Customers->FreeBookmark(SavePlace);
  };
}

/*
To ensure that the button is disabled when there is no
previous record, the OnDataChange event of the DataSource
detects when the user moves to the beginning of file (BOF
property becomes true), and disables the button.  Detection
occurs on scrolling and editing, not selection with the mouse.
*/
void __fastcall TForm1::DS2DataChange(TObject *Sender, TField *Field)
{
  if (Customers->Bof)
    Button2->Enabled = False;
  else
    Button2->Enabled = True;
}

Delphi Examples:

Copy Code

{
This example uses a button to copy the value of a field in
the previous record into the corresponding field in the
current record.  The field to copy is specified by using
FindField and the name of the field.
}
procedure TForm1.Button1Click(Sender: TObject);
var
   SavePlace: TBookmark;
   PrevValue: Variant;
begin
  Close;
   with Customers do
   begin
    { get a bookmark so that we can return to the same record }
    SavePlace := GetBookmark;
    try
      { move to prior record}
      FindPrior; 
      { get the value }
      { This is the safe way to get 'CustNo' field }
      PrevValue := FindField('Field2').Value;
      { This is *not* the safe way to change 'CustNo' field }
//    PrevValue := Fields[1].Value;
      { Move back to the bookmark
      this may not be the next record anymore
      if something else is changing the dataset asynchronously }
      GotoBookmark(SavePlace);
      { Set the value }
      Edit;
      { This is the safe way to change 'CustNo' field }
      FindField('Field2').AsString := PrevValue;
      { This is *not* the safe way to change 'CustNo' field }
//      Fields[1].AsString := PrevValue;
      { Free the bookmark }
    finally
      FreeBookmark(SavePlace);
    end;
  end;
end;

{
To ensure that the button is disabled when there is no
previous record, the OnDataChange event of the DataSource
detects when the user moves to the beginning of file (BOF
property becomes true), and disables the button.  Detection
occurs on scrolling and editing, not selection with the mouse.
}
procedure TForm1.DS2DataChange(Sender: TObject; Field: TField);
begin
  if Customers.Bof then
    Button1.Enabled := False
  else
    Button1.Enabled := True;
end;